This application is based upon Japanese Patent Application Nos. Hei. 11-202474 filed on Jul. 16, 1999 and Hei. 11-358329 filed on Dec. 17, 1999, the contents of which are incorporated herein by reference.
1. Field of the Invention
This invention relates to angular position detecting apparatuses, and particular to an angular position detecting apparatus which detects an angular position of a target detection object by using a magnetic detecting element.
2. Related Art
In this kind of angular position detecting apparatus, an angular position detecting apparatus as shown in, for example, JP A 61-75213 (see FIG. 22), has been proposed. According to this angular position detecting apparatus, a cylindrical magnet 1 is magnetized so that a magnetic field is formed in parallel therein. A magnetic detecting element 2 is positioned at a center portion of the magnet 1. The magnet 1 (parallel magnetic field) is rotated in response to a rotation of the target detection object. As a result, the amount of magnetic flux crossing the magnetic detecting element 2 is changed. An output signal from the magnetic detecting element 2 changes in proportion to the amount of the magnetic flux. The angular position xcex8m of the target detection object is detected based on an the output signal from the magnetic detecting element 2.
In the case where the angular position xcex8m of the target detection object is detected based on the output signal from the magnetic detecting element 2 in this way, and the detectable range of the angular position xcex8m is expanded, an output change characteristic of the magnetic detecting element 2 with respect to the angular position xcex8m needs to be linearly changed to a wider range as much as possible.
However, according to the conventional structure, since the parallel magnetic field is rotated with respect to the magnetic detecting element 2, the amount of magnetic flux, crossing the magnetic detecting element 2 decreases in accordance with a trigonometric function. As a result, the output change characteristic of the magnetic detecting element 2 with respect to the angular position xcex8m deviates from a line, and forms curves based on the trigonometric function (see FIG. BA). As a result, according to the conventional structure, a semi-linear output can be obtained within only a narrow range of the angular position xcex8m. Therefore, the output change characteristic of the magnetic detecting element 2 with respect to the angular position xcex8m becomes bad, and the detectable range of the angular position xcex8m becomes narrow.
This invention has been conceived in view of the background thus far described and its object is to provide an angular position detecting apparatus which can optionally determine an output change characteristic of the magnetic detecting element with respect to the angular position within a wide range and which can improve a detection characteristic of the angular position.
According to a first aspect of the present invention, a magnetic field is generated between a magnet and a yoke, and a magnetic detecting element is provided in the magnetic field. Here, the magnetic detecting element is offset from a rotation axis of a rotor. In this case, a relationship between an angle of magnetic flux crossing the magnetic detecting element and angular position of the rotor is changed. By using this change, an output change characteristic of the magnetic detecting element with respect to the angular position can be widely set. As a result, a detection characteristic of the angular position can be improved.
According to a second aspect of the present invention, each of the magnetic detecting elements has a range of an angular position in which an output characteristic becomes linear. The range is different from each other with respect to every magnetic detecting element. An output selector selectively generates outputs of a particular magnetic detecting element in a linear region, depending on the angular position. As a result, a detectable angle range, in which an output change characteristic of the angular position detecting apparatus becomes linear, can be considerably expanded compared to a case where the magnetic detecting element is only one.
According to a third aspect of the present invention, a magnet and a magnetic detecting element are arranged so that outputs of the magnetic detecting element becomes substantially zero at around a particular angular position at which detection accuracy is extremely required. Incidentally, according to the angular position apparatus using the magnetic detecting element, detection accuracy is best at a point where the output of the magnetic detecting element becomes zero. This is because the point where the output of the magnetic detecting element becomes zero is the center of the linear region of the outputs, and therefore the linearity becomes the best. Furthermore, when the output of the magnetic detection is zero, influence to the magnetic detecting element due to a thermal characteristic becomes small. Therefore, influence to the magnetic detecting element due to a thermal characteristic becomes small at around a particular angular position at which detection accuracy is extremely required. As a result, a detection characteristic of the angular position can be improved.